The Y-tunnus is Finland's business identity code — an 8-digit number written as seven digits, a hyphen, then a check digit. For VAT it is prefixed with FI, so a Finnish VAT number is FI followed by the Y-tunnus digits.

How is the Finnish VAT check digit calculated?

The first seven digits are multiplied by the weights 7, 9, 10, 5, 8, 4, 2 and summed. Taking the sum modulo 11 gives a remainder; the check digit is 11 minus that remainder, or 0 if the remainder is 0.

What does a remainder of 1 mean?

If the modulo-11 remainder is exactly 1, no valid check digit can be formed, so that combination of seven digits was never issued as a Y-tunnus. The tool reports the number as invalid in that case.

Do I need the FI prefix and hyphen?

No. You can enter the number with or without the FI prefix and with or without the hyphen. The tool strips them before computing the check digit.

Is my VAT number sent anywhere?

No. The check runs entirely in your browser in JavaScript. Nothing is transmitted, so the tool is safe for accounting and compliance use.

Finland VAT Number Validator

The Finland VAT Number Validator checks whether a Finnish VAT number is structurally valid by recomputing the modulo-11 check digit of the Y-tunnus business ID. It accepts the number with or without the FI prefix and the hyphen and tells you whether the check digit matches — all in your browser.

How it works

A Finnish VAT number is the prefix FI followed by the 8-digit Y-tunnus, which is normally written as 1234567-8. The last digit is a modulo-11 check that guards against transposition and typing errors.

The tool multiplies the first seven digits by the weights [7,9,10,5,8,4,2] and sums the products. It then takes the sum modulo 11. If the remainder is 0, the check digit should be 0. If the remainder is 1, no valid check digit exists and the number is reported invalid. Otherwise the expected check digit is 11 minus the remainder, and it must equal the eighth digit you entered.

Example

For FI 12345678 the tool derives the expected check digit from the first seven digits and compares it to the trailing 8. If they match, the Y-tunnus is internally consistent; if the weighting produces a remainder of 1, the tool explains that the combination is not issuable.

Notes

A valid check digit confirms the Y-tunnus is internally consistent — it does not confirm the business is currently VAT-registered. Check the YTJ business information system or the EU VIES service for live status before relying on the number for e-invoicing or intra-EU trade. Everything runs locally in your browser.